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Show measurements have been appl1ed to the isothermal flow model1ng of utl1lty furnace systems. These have incresed the accuracy of, as well as broadened the range over which such stud1es can be performed. Recent developments of significance to furnace flow modellng can be dlvn1ed Into three major areas: Flow visualization, Velocity measurement, and Tracer gas concentration measurements. Advances in each of these areas are discussed next. Flow Visualization Technlaues- Flow v1suallzat10n techniques are one of the oldest and most effective tools ava1lable for the evaluat10n of fluid dynamic phenomena and flow systems. A number of the available methods have direct appl1catlon to the study of aerodynamic patterns 1n isothermal furnace flow models, the most notable of these being the use of smoke tracers ( 11). Other techniques such as yarn tufts, neutral density helium bubbles (6), and the Injection of Ignited charcoal particles (12) have also been used successfully. As the Questions that must be answered through furnace flow modellng become more compfex, the flow visual1zation techniques used are becoming more quantitative in nature. That is, techniques are belng developed where not only are the overall flow patterns revealed, but simultaneous multiple-point measurements of flow field parameters such as velocity and tracer concentration can be obtained (13). Included in this category are the potential use of a laser light sheet (14), laser induced fluorescence (15), and lnfared video photography ( 16). Velocity Measurement Technigues- The measurement of velocities anad pressures are par~mount to improving the performance and/or efflclency of any part of the gas side of a utllity furna~e. 1his informat.ion Quantitatively details the dlrectlOn and magmtude of the flow field as well as the location and size of recirculation and low flow zones. Ve locity and total pressure measurements are used In determining the unit pressure drop of a furnace system, dfrectly related to operating power requirements. Determination of the extent of flow recirculation and turbulence intenSity are particularly Important in the area of burner development where large amounts of fuel and air mus~ be Quickly mixea whl1e maintaining burner stabl11ty and flame attachment. Regions of low flow where particulate dropout may occur can also be identified through velocity field ~easurements. Local velocity f1eld measurement 1S also used to predict gas side tube erosion. Also, isothermal flow modeling of furnace systems has been used to pre(jict the heat transfer performance of heat exchangers as a . funct ion of furnace gas flow patterns (91. Because of the three dimension character of the flow fields within most furnaces any velocity measurements must be resolved into three spatial components. Before the introduction of new technjQues, these measurements were obtained manually with multi-hole pitot tubes or 118 multlwlre hot wfre anemometers. These devices generally required that the velocity direction was obtained through the manual positioning and rotation of the probe to the point of maximum velocity before the data was recorded. Through the application of robotiCS, the probe positioning and rotation movements have been automatecf. Figure 1 shows such a system cal1ed the Automatic Probe Traversing Device (APTO). This system, a self contained programmable data acquisition system, automatically positions the multi-hole pftot tube and records all pressure readings Into computer memory. Fig. 1 - Automatic Probe Traversing Device Another new technique recently appl1ed to isothermal flow modeling is laser Doppler Anemometry (LOA). The baslc concept of applying lasers for velocity measuremen was first started in 1964 and, at the present time, LOA is the best known laser based diagnostic technique. The theoretical and operational background of laser anemometers are discussed in detail by Durst, et. a1. (17) and the references of Self anti Whitelaw (18) and Durst (19) provide a good review of LOA systems. Practical appl1cations of LOA are numerous- Table 1 gives a summary of some recent appl1catlons at Combustion Engineering. Also, as pOinted out by Chlgler (20), In many appllcatlons of aerodynamics and fluid flow, the laser anemometer has become the most accurate means of velocity measurement and has replaced the pltot tube and hot wire anemometer, which are both intrusive measurement techniques . |
